Plastic substrates have become the preferred substrates for large area electronics and optoelectronics because of their light weight, flexibility, shock resistance and low cost. To this end, the deposition of conducting or semi-conducting thin films on plastic substrates is of importance. For example, a semiconducting thin film (e.g., polycrystalline or amorphous silicon) is a base material for thin film transistors, which are the fundamental building blocks for large area electronics. A transparent conducting thin film (e.g., ITO: indium tin oxide) is a component for diverse optoelectronic devices that simultaneously involve high electrical conductivity and optical transparency, including liquid crystal displays, touch screen, organic light-emitting diodes (OLEDs) and solar cells. Current approaches to these thin films usually involve high temperature chemical vapor deposition (CVD) processes or high vacuum physical vapor deposition (PVD) processes, which are often too costly and often involve too high processing temperature to be compatible with plastic substrates.
For example, indium tin oxide (ITO) is currently the dominant material for transparent conductors and is typically formed by costly PVD approaches. However, the limited natural abundance of indium and the brittle nature of an ITO film pose a potential challenge for its application in future flexible devices. Additionally, ITO shows poor transparency in near-infrared (NIR) region due to free carrier absorption, and thus is unsuitable for infrared imaging, sensing, emission devices, or NIR-sensitive solar cells. On the other hand, CVD grown Bi2Se3 thin films can function as an excellent infrared transparent conductor. Bi2Se3 is a layered, narrow-bandgap semiconductor, and also a typical topological insulator with metallic surface state. Theoretical and experimental studies have revealed that conducting surface states in Bi2Se3 are concentrated within a few quintuple layer thickness (<about 6 nm). Therefore, Bi2Se3 nanostructures may represent a desirable material for the formation of highly conductive electronic thin films. Additionally, the topological insulator Bi2Se3 thin films can also exhibit an unusual infrared transparency property due to a forbidden direct photoexcitation within a surface state to make it an excellent NIR transparent conductor for infrared optoelectronics. However, these Bi2Se3 thin films studied to date are typically obtained by a CVD approach, which involves stringent synthetic conditions including specific substrates (e.g., mica), high temperature and vacuum, which are difficult and costly to scale for large area production on plastic substrates.
It is against this background that a need arose to develop embodiments of this disclosure.